As one of typical ceramic electronic components, there is a multilayer ceramic capacitor that has a structure, for example, as shown in FIG. 3.
This multilayer ceramic capacitor has, as shown in FIG. 3, a structure with external electrodes 54 (54a, 54b) provided so as to be electrically connected to a plurality of internal electrodes 52 (52a, 52b) on both end surfaces 53a, 53b of a ceramic laminated body (multilayer ceramic element) 60 that has the internal electrodes 52 (52a, 52b) laminated with ceramic layers (ceramic dielectric layers) 51 interposed between the internal electrodes.
In recent years, multilayer ceramic capacitors have been expanded in intended use, while the usage environments have increasingly become severe. Further, requests for characteristic enhancements have also increased, such as a reduction in size and an increase in capacitance.
Further, the increase in capacitance for multilayer ceramic capacitors is achieved by making dielectric elements thinner. This is also accompanied by increased effective areas and increased electric field intensities applied to the elements.
Thus, in order to ensure reliability in a thin layer and at a high electric field intensity while keeping the relative permittivity of a dielectric high, a dielectric ceramic is used which has a so-called core-shell structure with a minute amount of an additive component as a solid solution on the outer periphery of ceramic particles, for example, such as a barium titanate-based ceramic.
However, multilayer ceramic capacitors that use a ceramic having a core-shell structure as dielectric layers have, when have a region where no additive component is present at grain boundaries, a problem when a high electric field is applied to the region. In such a case, the electric field is concentrated on specific points of the ceramic dielectric layers, thereby accelerating degradation of insulation resistance.
Therefore, in order to ensure the reliability, it is important to decrease the proportion of grain boundaries at which the additive component is not present as a solid solution.
Under these circumstances, as a multilayer ceramic capacitor which has an increased high-temperature load life even when dielectric layers are reduced in thickness, a multilayer ceramic capacitor has been proposed which includes a plurality of dielectric layers composed of barium titanate-based crystal grains, a plurality of internal electrode layers containing nickel as their main constituent, formed between the dielectric layers, and external electrodes electrically connected to the internal electrode layers, and has center mean line roughness Rac of 20 nm or more and 100 nm or less at the interfaces between the dielectric layers and the internal electrode layers (see Patent Document 1).
More specifically, this multilayer ceramic capacitor is intended to suppress insulation resistance degradation of the multilayer ceramic capacitor under high temperature and high electric field, in a way that the asperity at the interfaces between the dielectric layers and the internal electrode layers is defined to fall within a predetermined range.
Further, Patent Document 1 mentions, in an example thereof, the use of a BaTiO3 powder of 0.15 μm in average particle size as a ceramic powder for dielectric green sheets for use in the manufacture of the multilayer ceramic capacitor, and the use of a glass powder containing SiO2 of 0.1 μm in average particle size as its main constituent as a sintering aid. In this case, in the process of firing, a solid solution of additive elements in BaTiO3 as a main raw material is believed to be achieved by turning into a liquid phase with, as a starting point, glass containing SiO2 as its main constituent, and incorporating Y, Mn, Mg added to the liquid phase.
However, in the case of the composition as mentioned above, the BaTiO3 powder as a main raw material is close in particle size to the glass powder containing SiO2 as its main constituent, which serves as a starting point for the liquid phase. Thus, glass particles inhomogeneously containing SiO2 as its main constituent will be present around the BaTiO3 particles, and carrying out firing in the condition is believed to also cause the solid solution of the additive elements in BaTiO3 to become inhomogeneous. Further, the dielectric ceramic in which the solid solution of the additive elements in BaTiO3 is inhomogeneous becomes more likely to cause degradation of insulation resistance under high temperature and high electric field.
Therefore, in the multilayer ceramic capacitor with the above-mentioned dielectric ceramic as dielectric layers, which is prepared by the method according to the example in Patent Document 1 mentioned above, degradation of insulation resistance is believed to be caused under high temperature and high electric field.
Patent Document 1: Japanese Patent Application Laid-Open No. 2007-173714